Identification of houses by personnel responding to emergency calls has been a long-standing problem. House numbers are frequently attached to the house itself, and these are consequently often difficult to see from a distance or from a passing vehicle. This problem is particularly pronounced at night, when even a prominent house number may be difficult or impossible to see. Consequently, emergency service personnel such as ambulance drivers, firemen, or policemen often lose precious minutes in identifying the proper home during an emergency.
A number of devices have been proposed for identifying or drawing attention to a structure in an emergency. Predominantly, these have taken the form of dedicated systems which serve no other function apart from that of providing an emergency signal.
Because they are dedicated systems, these devices share a number of disadvantages for use in a residential environment due to their expense and the need for special display fixtures, mounting, and wiring.
Many of these drawbacks could be avoided by making use of a pre-existing system having some other primary function, with the alarm function being provided as a secondary function for use in an emergency. In this respect, a great majority of residential dwellings are provided with conventional porch lights which have the primary function of illuminating the entrance of the house which faces the street, and these are clearly visible to passing personnel. Also, the porch light frequently serves to illuminate the house number so that it can be read from the street. One attempt which has been made to utilize such porch lights to serve an alarm function is that disclosed in U.S. Pat. No. 4,730,184 (issued Mar. 8, 1988 to Bach), which shows an alarm assembly 80 which screws into a conventional porch light receptacle 89. The device consists of a sound generating assembly 82 which screws directly into the receptacle, and a light bulb 83 which screws into a second receptacle which is provided in the sound generating assembly. A "flasher unit" which periodically interrupts the flow of current therethrough is inserted in each of the receptacles, consequently causing the sound generating portion to pulsate, and the light bulb to flash on-and-off, whenever the porch light switch is turned on. A significant drawback of this device, of course, is the fact that once it has been installed in the porch light socket, this fixture can no longer be used as a conventional porch light to illuminate the porch area, which was the primary purpose for which it was originally installed.
Another, more sophisticated device which has been proposed for flashing the porch light of a house in a danger situation is that disclosed in U.S. Pat. No. 4,556,863 (issued Dec. 3, 1985 to Devitt et al.). This shows a switch device which is designed to be installed in a switch box in place of a conventional on/off switch, for the purpose of allowing a porch light to be flashed continuously on and off, as well as for permitting the light to be turned on and off in a conventional manner. Although this general approach is quite desirable from the standpoint of economy and convenience of installation, the actual switching circuitry taught by the Devitt patent encumbers the device with several serious drawbacks. This device employs a power switcher which is periodically enabled and disabled by an oscillator, with DC power for operating these components being stored in a capacitor 71 which charges up only during those intervals when the power switcher is not conducting. This is because the switcher acts as a short circuit in parallel with the supply to the capacitor during the period it is conducting, causing the main current to bypass the supply; but, during this same period the capacitor is discharging in order to supply power to the oscillator and buffer circuits to keep the switcher actuated. The light bulb can thus only be kept on until the energy stored in the capacitor has been used up, at which point the main light bulb must be switched off so that the capacitor can be charged up again. Since the current to charge up the capacitor must flow through a step-down resistor 69, the resistor will tend to overheat if this flow of current is very great. Consequently, the impedence of this resistor must be kept relatively high in order to keep the flow of current relatively low, but the net effect of this is that the charge-up rate of the capacitor is also kept very slow, and then the capacitor discharges relatively quickly when keeping the power switcher actuated. As a result, the Devitt device can only operate on a very limited duty cycle when flashing the porch light: this duty cycle (i.e., the ratio of the time interval the load is on to the sum of the intervals during which the load is on and off) may only be about 10-20%, and the practical affect of this is that the porch light is turned on for only short, dim flashes, which may be inadequate to effectively draw the attention of emergency response personnel to the house, or to illuminate address numbers so that they can be verified. Incidentally, if one were to attempt to overcome this deficiency by employing a resistor which would permit current to flow through it at a rate sufficient to significantly increase the duty cycle of the Devitt device (without the resistor overheating), this would necessitate use of a much larger resistor (e.g., on the order of 2 inches in height), which would tend to make it difficult or impossible to build the switching device so that it could fit in a conventional junction box.
Moreover, the majority of prior devices have required manual operation of the switch in order to activate the emergency mode of the system. This can be a disadvantage in some emergency situations, where the occupant is usually preoccupied with caring for the injured person and is sometimes in a near-panic condition. In short, while the occupant usually remembers to call "911", they may forget to take the additional step of actuating a separate switch mechanism.
Accordingly, there exists a need for an inexpensive and effective system for drawing attention to a residence or other building in which an emergency situation exists, and which selectively provides this alarm function automatically in response to the dialing of a designated emergency telephone number, by flashing a conventional porch light or the like on-and-off, yet which permits that light to selectively function in its normal on/off modes as well. Furthermore, there exists a need for such a device which flashes the light on-and-off with a sufficient duty cycle that it provides an effective emergency signal, as well as adequate illumination of the building entrance and its associated address numerals to permit these to be clearly observed by emergency response personnel. Still further, a need exists for a telephone-controlled electrical switch which can be used in a conventional switch box installation and which will provide substantially full electrical power to the lights or other electrical load.